Metals above carbon in the reactivity series
2 marks · HardChromium can be extracted from chromium(III) oxide by heating it with aluminium powder. Describe how this reaction shows the use of a more reactive metal in extraction, and explain why aluminium is used instead of carbon.
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Also accept: Aluminium reduces chromium(III) oxide because it is more reactive than chromium, displacing chromium from its oxide.; Aluminium is more reactive than chromium and can remove the oxygen from chromium oxide; carbon cannot do this for metals above it.
Common mistakes: Saying aluminium is used because it is less reactive.; Confusing reduction with oxidation for the metals.
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Marking points
M1 · 1 mark · States that aluminium is a more reactive metal that removes oxygen from chromium(III) oxide (or displaces chromium from the oxide).
A1 · 1 mark · Explains why aluminium is used instead of carbon (aluminium is more reactive than chromium and carbon; carbon cannot reduce chromium oxide).
Worked solution
Aluminium is used to extract chromium from chromium(III) oxide because aluminium is more reactive than chromium. It removes the oxygen from chromium(III) oxide by reduction, forming aluminium oxide and chromium metal:
Carbon cannot be used for this extraction because carbon is less reactive than chromium and cannot remove oxygen from chromium(III) oxide.